1. Field of the Invention:
The present invention relates to a process for producing a fluorinated acid fluoride having an ester group, more particularly, it relates to a novel process for producing a fluorinated acid flouride having an ester group by a reaction of a specific diacid fluoride with an alcohol.
2. Description of the Prior Arts
The flourinated acid flourides of the present invention have the formula ##STR3## wherein A represents a C.sub.1 -C.sub.10 bifunctional perfluoro group; p represents 0 or 1; q represents an integer of 1 to 8; and R represents an organic group.
The fluorinated acid fluoride having an ester group can be produced by the novel reaction of the specific diacid fluoride with an alcohol ##STR4## wherein A,p,q and R are defined above.
The monoesters of fluorinated acid fluoride produced by the process of the present invention are useful as intermediates for producing various fluorinated compounds especially various fluorinated compounds having a terminal ester group.
For example, perfluorovinyl ethers having an ester group can be obtained by the thermal decomposition of the monoesters of fluorinated acid fluoride as disclosed in Japanese Unexamined Patent Publication Nos. 83417/1977 and 105118/1977, etc.
The alkali metal salts of fluorinated carboxylic acid having an ester group can be obtained by reacting the fluorinated acid fluorides having an ester group with an alkali metal carbonate and the alkali metal salts can be thermally decomposed as disclosed in Japanese Unexamined Patent Publication Nos. 78826/1977 and 78827/1977.
The diacid fluorides used in the process of the present invention can be obtained by the reaction disclosed in Japanese Unexamined Patent Publication No. 3017/1977, etc.
The specific diacid fluorides can also be obtained by reacting .alpha.,.omega.-diiodo-perfluoroalkane or a perfluoro acid fluoride having a terminal iodo group with fuming sulfuric acid to obtain diacid fluorides disclosed in Japanese Unexamined Patent Publication Nos. 23020/1977 and 39605/1977 and then reacting the diacid fluoride with hexafluoropropylene epoxide.
The diacid fluorides can be also obtained by converting perfluorodicarboxylic acid dichlorides to difluorides in a polar solvent with NaF or KF and reacting the difluorides with hexafluoropropylene epoxide.
Alcohols as the other raw materials can be obtained from various sources as well-known. Usually, it is preferable to use the alcohols having the formula ROH wherein R is a group having 1 to 8 carbon atoms and can be in a straight chain form or a branched chain form.
The inventors have found that the acid fluorides having an ester group which have the formula FOC--CO.sub.2 R or FOC--A--CO.sub.2 R can be obtained by the reaction of dicarboxylic acid fluoride having the formula FOC--COF or FOC--(CF.sub.2).sub.n --COF wherein n represents an integer of 1 to 10 with an alcohol having the fomula ROH as disclosed in Japanese Patent Application No. 113712/1976.
The inventors have studied various reactions of the dicarboxylic acid difluorides with the alcohols. As the results, the interesting phenomenon of the present invention has been found.
The reactivity of carbonyl fluoride groups (--COF group) at both terminals to the alcohol is remarkably different depending upon the presence of --CF.sub.3 group at the .alpha.-position to the carbonyl carbon.
The esterification with the alcohol is selectively performed for --COF group having no --CF.sub.3 group at the .alpha.-position. In order to effectively and smoothly produce the monoesters of acid fluoride, it is preferable to use the specific asymmetrical diacid fluorides as the raw material.
In general, it is easily considered that perfluoro-2-methyl-3-oxa-heptanoyl difluoride having the formula ##STR5## is an asymmetrical compound and the carbonyl carbons of the --COF groups at both terminals are expected to have different electrophilic property depending upon the presence of --CF.sub.3 group at .alpha.-positions.
When the monoesterification with the alcohol is considered, the alkoxy group will attack the carbonyl carbon showing higher electrophillic character by --CF.sub.3 group at the .alpha.-position, in a nucleophilic manner, whereby 1-carboalkoxy-perfluoro-2-methyl-3-oxa-hexanoyl fluoride having the formula ##STR6## will be selectively produced.
The inventors have further studied the esterification in the system containing CsF, KF or NaF. As the results, the mole ratio of ##STR7## on the resulting product is 1/4.4 in the system of KF; and 1/6.1 in the system of NaF.
When the monoesterification is carried out in the system diluting the raw materials with the non-polar solvent, it has been found that the mole ratio of ##STR8## is in a range of 1/18 to 1/50.
These descriptions are to clearly understand the present invention without any intention to limit the scope of the present invention.